Reynolds number effects on mixing and combustion in a reacting shearlayer

Mungal, M. G.; Hermanson, James C.; Dimotakis, Paul E.

doi:10.2514/3.9101

Cited by 57 publications

(22 citation statements)

References 16 publications

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“…a reduced downstream growth rate. This behaviour for co-flowing freestreams was confirmed by the work of Browand & Latigo (1979), Weisbrot, Einav & Wygnanski (1982), and Mungal, Hermanson & Dimotakis (1985). See also additional discussion and references in the review paper by Dimotakis (1991).…”

Section: Introductionsupporting

confidence: 53%

Turbulent shear-layer mixing at high Reynolds numbers: effects of inflow conditions

1998

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We report on the results from a set of incompressible, shear-layer flow experiments, at high Reynolds number (Re δ ≡ ρ ∆U δ T (x)/µ 2 × 10 5 ), in which the inflow conditions of shear-layer formation were varied (δ T is the temperature-rise thickness for chemically-reacting shear layers). Both inert and chemically-reacting flows were investigated, the latter employing the (H 2 +NO)/F 2 chemical system in the kineticallyfast regime to measure molecular mixing. Inflow conditions were varied by perturbing each, or both, boundary layers on the splitter plate separating the two freestream flows, upstream of shear-layer formation. The results of the chemically-reacting 'flip experiments' reveal that seemingly small changes in inflow conditions can have a significant influence not only on the large-scale structure and shear-layer growth rate, as had been documented previously, but also on molecular mixing and chemicalproduct formation, far downstream of the inflow region.

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Section: Introductionsupporting

confidence: 53%

Turbulent shear-layer mixing at high Reynolds numbers: effects of inflow conditions

1998

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“…According to our results, the homogeneous region and the flame sheets contribute equally to the total product in a gas-phase layer. It should be mentioned that the amount of product in gas-phase layers is a weak function of Reynolds number and decreases by 20% for a factor of 10 increase in Reynolds number as reported by Mungal, Hermanson & Dimotakis (1985). The amount of product in a liquid layer has a much weaker dependence on Reynolds number as evidenced by experimental results and also suggested by the Broadwell-Breidenthal model.…”

Section: Amount Of Productmentioning

confidence: 66%

Mixing and chemical reactions in a turbulent liquid mixing layer

1986

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An experimental investigation of entrainment and mixing in reacting and nonreacting turbulent mixing layers at large Schmidt number is presented. In nonreacting cases, a passive scalar is used to measure the probability density function (p.d.f.) ofthe composition field. Chemically reacting experiments employ a diffusionlimited acid-base reaction to directly measure the extent of molecular mixing. The measurements make use of laser-induced fluorescence diagnostics and high-speed, real-time digital image-acquisition techniques.Our results show that the vortical structures in the mixing layer initially roll-up with a large excess of fluid from the high-speed stream entrapped in the cores. During the mixing transition, not only does the amount of mixed fluid increase, but its composition also changes. It is found that the range of compositions of the mixed fluid, above the mixing transition and also throughout the transition region, is essentially uniform across the entire transverse extent of the layer. Our measurements indicate that the probability of finding unmixed fluid in the centre of the layer, above the mixing transition, can be as high as 0.45. In addition, the mean concentration of mixed fluid across the layer is found to be approximately constant at a value corresponding to the entrainment ratio. Comparisons with gas-phase data show that the normalized amount of chemical product formed in the liquid layer, at high Reynolds number, is 50% less than the corresponding quantity measured in the gas-phase case. We therefore conclude that Schmidt number plays a role in turbulent mixing of high-Reynolds-number flows.

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“…Thus, strictly speaking, comparisons between gases and liquids, or between gases at different Reynolds numbers, should only be made with this restriction in mind. The dependence upon Reynolds number of the amount of product formed in a gas has been reported by Mungal, Dimotakis & Hermanson (1984). There it was found that the amount of product decreased by 20% for a factor of 10 increase in Reynolds number (or 6% per factor of 2).…”

Section: Broadwell-breidenthal Modelmentioning

confidence: 79%

Mixing and combustion with low heat release in a turbulent shear layer

1984

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Turbulent mixing and combustion are investigated in a gaseous shear layer formed between two streams: one containing a low concentration of hydrogen in nitrogen and the other containing a low concentration of fluorine in nitrogen. The resulting temperature field is measured simultaneously at eight points across the width of the layer using fast-response cold-wire thermometry. The results show the presence of large, hot structures separated by tongues of cool fluid that enter the layer from either side. The usual bell-shaped mean-temperature profiles therefore result from a duty cycle whereby a fixed probe sees alternating hot and cool fluid, which results in the local mean. The adiabatic flame temperature is not achieved in the mean, at any location across the layer. For fixed velocities, it is found that, in general, two different mean-temperature profiles result from a given pair of reactant compositions if the sides of the layer on which they are carried are exchanged ('flipped'). This finding is a direct consequence of the asymmetric entrainment of fluid into the layer. Results are compared with the predictions of Konrad and discussed in the context of the Broadwell-Breidenthal model. By comparison with the liquid result of Breidenthal, the amount of product formed in the layer at high Reynolds number is found to be dependent upon the Schmidt number. Results for a helium-nitrogen layer are discussed briefly.

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Reynolds number effects on mixing and combustion in a reacting shearlayer

Cited by 57 publications

References 16 publications

Turbulent shear-layer mixing at high Reynolds numbers: effects of inflow conditions

Turbulent shear-layer mixing at high Reynolds numbers: effects of inflow conditions

Mixing and chemical reactions in a turbulent liquid mixing layer

Mixing and combustion with low heat release in a turbulent shear layer

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